There are a number of fundamental limitations with conventional mechanical conveyor systems such as those which employ a belt for transporting pallets between processing stations. First, the speed of the belt is typically quite limited. This is largely due to the fact that the pallets are typically stopped by mechanical stop mechanisms, e.g., in order to be processed at a processing station. Thus, if the belt conveyor is operated at a high speed, the strong impact between a pallet and mechanical stop is likely to jar whatever parts the pallet may be carrying for processing. Second, it is generally not possible to vary the acceleration and velocity profiles for individual pallets. For instance, if a first pallet is empty and a second pallet is loaded with delicate parts, it is generally not possible to aggressively accelerate the first pallet to a high speed while controlling the second pallet using more gentle acceleration and a differing velocity profile. This limitation may affect the latency and the throughput of the manufacturing line because empty pallets will generally have to flow through at the same rate as the loaded pallets. Third, a belt conveyor is typically not bidirectional, which may result in a suboptimal design of the manufacturing line. Fourth, the belt conveyor typically provides limited flexibility or programmability, such as being able to have multiple stopping locations at one processing station or being able to very quickly change the positions of processing stations when the line is adjusted/changed. Finally, the data acquisition capabilities provided by the belt conveyor are typically quite limited. For example, it is typically not possible to know where the pallets and their constituent loads are located along the conveyor at all times. Thus, for instance, it may be difficult to know how many pallets are queued at a particular processing station.
Conventional conveyor systems making use of scroll cams are also known but have some limitations as well. For example, scroll cam systems may have or develop reduced positional repeatability due to existing or developed play in the cam grooves. Scroll cam systems also have generally no or very limited flexibility or programmability.
For these and other reasons, a conveyor system having multiple moving elements or pallets under substantially independent control may be desirable for various types of applications.
Conveyor systems having multiple pallets under substantially independent control are known in the art, but suffer from a variety of limitations. For example, in some cases involving linear motors, the carts or pallets cannot be positioned to stop at any point along the conveyor, but only where linear motors are disposed. This makes changing the location of a station a troublesome endeavour. In addition, it is difficult to pinpoint the location of a moving pallet at any time.
In another conventional system involving a moving-magnet type linear d.c. brushless motor having plural moving elements disposed for motion along a track, the fact that a separate track of position/commutation sensors is required for each moving element means that the system can only accommodate a relatively small number of moving elements. Second, the length of the linear motor is limited by a servo-control mechanism, described as a single microcomputer, which can only process and accommodate a limited number of the position/commutation sensors and associated electric current generating control circuitry. Third, the winding arrangement of the stator armature is essentially that of a linear stepper motor, which presents an uneven magnetic reluctance along the stator armature resulting in relatively noticeable cogging effects and a jerky thrust production. Finally, the, coreless design of the stator armature also results in a relatively low average thrust production which may not be suitable for typical conveyor system applications.
Some conventional conveyor systems that have independent control have drawbacks with regard to space limitations and/or material requirements. For example, some magnetic oriented conveyors are not able to bypass rejects or empty pallets or bypass an unload station when a reject or empty pallet is discovered. Some conventional conveyor systems require a larger footprint because of requirements that an entire loop be available for pallet movement or extra modules are needed for part loading/unloading stations.
While independently controlled conveyor systems can have various benefits, cost concerns will often dictate a need for lower priced conventional mechanical conveyors, depending on the conveying application involved.